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Sex and aggression linked in male mouse brains but not in female

Get out of my way!

VictorTyakht/Getty

By Jessica Hamzelou

Aggression and sexual behaviour are controlled by the same brain cells in male mice – but not in females. The finding suggests that males are more likely to become aggressive when they see a potential mate than females.

The brain regions that contain these cells look similar in mice and humans, say the researchers behind the study, but they don’t yet know if their finding has relevance to human behaviour.

Similar to humans, male mice are, on the whole, more aggressive than females. Because of this, most research into aggression has overlooked females, says Dayu Lin at New York University. “I would say 90 per cent of aggression studies have been done in males,” she says. “We know very little about aggression in females.”

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But females can be aggressive too. For instance, female mice can be aggressive when protecting their newborn pups.

Sex and aggression

In 2011, Lin and her colleagues studied a region of the brain called the hypothalamus, responsible for regulating many different behaviours. They discovered a set of cells within this region in male mice that controlled both aggressive and sexual behaviours. When the cells were shut off, the mice didn’t mate or show aggression, but both behaviours could be triggered when the cells were stimulated.

Now, they have shown that the cells controlling these behaviours are separate in female mice, in both those that haven’t mated and new mothers. The cells for aggression are close to the centre of the hypothalamus, while cells for sexual behaviour are at the edge, says Lin. “But in the male, the cells are totally mixed up and overlap.”

This might be because some aspects of mating resemble aggression for male mice, says Lin. A male mouse will have to approach a female and mount her, for instance. Female mice stay still for mating, which looks nothing like aggression.

Mouse vs human

Can the finding apply to humans? The hypothalamus looks very similar across species, says Lin. “These regions are very conserved in birds, crocodiles and monkeys,” she says. “There’s no reason for me to think that humans are unique.”

But Daphna Joel at Tel Aviv University in Israel doesn’t think it can be easily applied to humans. “Sexual and aggressive behaviours are complex and context-dependent in mice, and of course much more so in humans,” she says.

The difference seen between the male and female hypothalamus in mice doesn’t mean that there are two types of brain, either, says Joel, whose own research suggests that there is no such thing as a “female brain” or “male brain”.

Some research suggests that the hypothalamus can look quite different in mice and humans, says Joel. Plus other regions that are known to look different in male and female mouse brains have “considerable overlap” in the brains of women and men, she says.